JP2018156758A - Insulation sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation sheet that has both of excellent electrical insulating performance and excellent thermal conductivity, also has excellent hydrolysis resistance, and further has excellent heat resistance and flexibility.SOLUTION: An insulation sheet contains a fibrous material, an inorganic particle, and a binder resin, the insulation sheet satisfying the following (i)-(iii): (i) a thickness of 20 μm or more and 400 μm or less; (ii) a thermal diffusion rate in thickness direction of 1×10-7 m/s or more; (iii) a breakdown voltage of 25 kV/mm or more.SELECTED DRAWING: None

Description

  The present invention relates to an insulating sheet.

In recent years, while competing on an international scale in the field of electrical equipment such as electric motors, generators and transformers, and in the field of electronic equipment such as integrated circuits and transistors, cost reduction of our products and differentiation from other companies' products, For the purpose of responding to advanced quality requirements from users, higher performance such as larger capacity and smaller size is required. The downsizing and high performance of electrical / electronic devices are accompanied by an increase in the amount of heat generated during use, and there is a problem that when the heat is accumulated, the operating efficiency of the device decreases due to temperature rise. Therefore, a heat countermeasure that conducts and dissipates the heat generated inside is important, and an electrical insulating material with improved thermal conductivity is strongly desired. Conventionally, as an insulating sheet used for this application, a sheet (Patent Document 1) including a resin having rubber elasticity, which is reinforced by a molded body made of a fibrous organic compound and an inorganic filler, has flexibility. A heat-dissipating insulating sheet (Patent Document 2), a heat-resistant polymer material, a binder, and a high-thermal-conductivity substance obtained by blending an epoxy resin and its curing agent with a filler that improves thermal conductivity into a sheet and curing it A manufacturing method of an aramid composite sheet in which the weight ratio of each constituent component is defined for non-woven fabric for laminated board (Patent Document 3), aramid fibrid, aramid floc, mica particles, and thermally conductive inorganic particles (Patent Document 3) 4) etc. are disclosed.

Japanese Patent No. 2732822 JP 1989-186520 A Japanese Patent No. 3250497 Patent No. 3660765

However, in the manufacturing method of the sheet | seat disclosed in patent document 1, patent document 3, and patent document 4, the nonwoven fabric for laminated boards, and an aramid composite sheet, the thin film property of a sheet | seat, heat dissipation, workability, and insulation are paralleled. There was a problem that it was difficult. Moreover, since an aramid resin is easy to hydrolyze, there exists a problem that it cannot endure long-term use. Moreover, in patent document 2, since it is a sheet | seat which bonded the sheet | seat which hardened | cured the epoxy resin, and the glass cloth, it was easy to produce a crack at the time of a process, and there existed a problem in workability.
Therefore, an object of the present invention is to provide an insulating sheet having both electrical insulation and thermal conductivity, excellent hydrolysis resistance, and excellent heat resistance and workability.

  Another object of the present invention is to provide an electrical device having improved heat dissipation characteristics by including such an insulating sheet.

In order to solve the above-mentioned problems, the thin-film heat-insulating insulating paper of the present invention employs the following means.
(1) An insulating sheet containing a fibrous material, inorganic particles, and a binder resin, and satisfying the following (i) to (iii).

(I) The thickness is 20 μm or more and 400 μm or less (ii) The thermal diffusivity in the thickness direction is 1 × 10 ⁻⁷ m ² / s or more (iii) The dielectric breakdown voltage is 25 kV / mm or more (2) The fibrous material is polyphenylene The insulating sheet according to (1), comprising sulfide.
(3) The insulating sheet according to any one of (1) and (2), comprising a fibrous material having an orientation parameter of less than 1.5 and a fibrous material having an orientation parameter of 1.5 or more.
(4) The insulating sheet according to any one of (1) to (3), wherein an average fiber diameter D1 of the fibrous material is 5 μm or more and 50 μm or less.
(5) The insulating sheet according to any one of (1) to (4), wherein an average particle diameter D2 of the inorganic particles is 0.1 μm or more and 20 μm or less.
(6) The average fiber diameter D1 (μm) of the fibrous material and the average particle diameter D2 (μm) of the inorganic particles satisfy 2 ≦ D1 / D2 ≦ 10 (1) to (5) Insulation sheet.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the insulating sheet which has electrical insulation and heat conductivity, is excellent in hydrolysis resistance, and is further excellent in heat resistance and workability.

  The insulating sheet of the present invention is an insulating sheet containing a fibrous material, inorganic particles, and a binder resin, and is characterized by satisfying the following (i) to (iii).

(I) The thickness is 20 μm or more and 400 μm or less (ii) The thermal diffusivity in the thickness direction is 1 × 10 −7 m ² / s or more (iii) The dielectric breakdown voltage is 25 kV / mm or more. To do.

It is important that the insulating sheet of the present invention has a thickness of 20 μm or more and 400 μm or less. If the thickness is less than 20 μm, the insulating properties may be significantly deteriorated. If the thickness exceeds 400 μm, workability may be significantly deteriorated. From the viewpoint of workability, insulation, and improvement of heat dissipation characteristics of electrical equipment, it is particularly preferably 20 μm or more and 300 μm or less.
Moreover, it is important for the insulating sheet of the present invention that the thermal diffusivity in the thickness direction is 1 × 10 ⁻⁷ m ² / s or more. From the viewpoint of heat dissipation of electrical equipment, the thermal diffusivity in the thickness direction is preferably 1.1 × 10 ⁻⁷ m ² / s or more, and 1.2 × 10 ⁻⁷ m ² / s or more. Is more preferable.
Examples of the method for setting the thermal diffusivity in the thickness direction within the above range include forming the insulating sheet from fibrous materials, inorganic particles, and a binder resin described later.

  Further, it is important that the insulation sheet of the present invention has a dielectric breakdown voltage of 25 kV / mm or more. When the dielectric breakdown voltage is less than 25 kV / mm, the insulating property may be insufficient when used as an insulating material for electric / electronic devices. The dielectric breakdown voltage is preferably 30 kV / mm or more, and more preferably 35 kV / mm or more. Examples of the method for setting the dielectric breakdown voltage within the above range include forming the insulating sheet from a fibrous material, inorganic particles, and a binder resin described later.

The fibrous material of the present invention is a filamentous material and has an aspect ratio of 1000 or more.
The fibrous material contained in the insulating sheet of the present invention is preferably a wet nonwoven fabric made of polyphenylene sulfide, a polyphenylene sulfide fibrous material having an orientation parameter of less than 1.5, and a polyphenylene sulfide fibrous material having an orientation parameter of 1.5 or more. It is preferable to contain. All the polyphenylene sulfide fibrous materials constituting the wet nonwoven fabric are 20 mass% or more and 100 mass% of polyphenylene sulfide fibrous materials having an orientation parameter of less than 1.5 from the viewpoint of firmly fusing the fibrous materials together by heating. % Is preferably 25% by mass or more and 100% by mass or less, and more preferably 25% by mass or more and 75% by mass or less.
Here, the orientation parameter is obtained by measuring the cross section of the insulating sheet by Raman spectroscopy, and is defined by the intensity ratio of peaks having a strong sensitivity to anisotropy.
The orientation parameter is an index of molecular orientation / crystallization, and the higher the orientation parameter, the more the molecule is oriented / crystallized.
When there are a plurality of peaks having a strong sensitivity to anisotropy, such as when a plurality of resins are mixed, the orientation parameter is obtained using the peak with the highest peak intensity.

  Moreover, as a fiber length of a fibrous material, the range of 1 mm or more and 20 mm or less is preferable. By setting it to 1 mm or more, the strength of the wet nonwoven fabric can be increased by entanglement of the fibers. Moreover, by setting it as 20 mm or less, it can prevent that a fiber etc. become a lump etc. and a nonuniformity etc. arise in a wet nonwoven fabric.

The basis weight of the fibrous material of the present invention is preferably 5 g / m ² or more and 200 g / m ² or less, more preferably 10 g / m ² or more and 200 g / m ² from the viewpoint of the impregnation property of the binder and the filling property of the inorganic particles. m ² , more preferably 10 g / m ² or more and 150 g / m ² or less.
The average fiber diameter D1 of the fibrous material of the present invention is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 20 μm or less, from the viewpoint of the impregnating property of the binder.

  The polyphenylene sulfide constituting the fibrous material of the present invention is a polymer containing phenylene sulfide units such as p-phenylene sulfide units and m-phenylene sulfide units as repeating units. The polyphenylene sulfide in the present invention may be a homopolymer of any one of these units or a copolymer having both units. Further, it may be a copolymer with other aromatic sulfide, but preferably 70 mol% or more of the repeating units are composed of p-phenylene sulfide.

  The average molecular weight of polyphenylene sulfide used for the fibrous material is preferably 40000 or more and 60000 or less. By setting it to 40000 or more, good mechanical properties can be obtained as a fibrous material. Further, the viscosity of 60000 or less is preferable because the viscosity of the melt spinning solution can be suppressed and a special high pressure resistant spinning equipment is not required.

As for content of the fibrous material contained in the insulating sheet of this invention, 10 volume% or more and 70 volume% or less are preferable. If the content of the fibrous material is less than 10% by volume, the insulating sheet may be broken at the time of processing or use, and the handleability may be deteriorated. If it exceeds 70% by volume, it may be difficult to take up inorganic particles or a binder. More preferably, it is 10 volume% or more and 60 volume% or less, More preferably, it is 10 volume% or more and 50 volume%.
The inorganic particles contained in the insulating sheet of the present invention are gold, silver, copper, platinum, palladium, rhenium, vanadium, osmium, cobalt, iron, zinc, ruthenium, praseodymium, chromium, nickel, aluminum, tin, zinc, titanium Metals such as tantalum, zirconium, antimony, indium, yttrium, lanthanum, zinc oxide, titanium oxide, cesium oxide, antimony oxide, tin oxide, indium tin oxide, yttrium oxide, lanthanum oxide, zirconium oxide, aluminum oxide, oxide Metal oxides such as magnesium and silicon oxide, metal fluorides such as lithium fluoride, magnesium fluoride, aluminum fluoride and cryolite, metal phosphates such as calcium phosphate, carbonates such as calcium carbonate, barium sulfate, sulfuric acid Magne Sulfates such as um, nitrides such as silicon nitride, boron nitride and carbon nitride, silicates such as wollastonite, sepiolite and zonotlite, titanates such as potassium titanate and strontium titanate, carbon, fullerene and carbon Examples thereof include carbon compounds such as fibers, carbon nanotubes, and silicon carbide. These inorganic particles may be used alone or in combination of two or more. These inorganic particles are surface-modified by surface treatment such as silane coupling agent treatment, metal deposition, polymer grafting, plasma treatment, etc. for the purpose of enhancing affinity with resin and enhancing dispersibility. It may be used.

In view of the fact that the insulating sheet of the present invention is often used in applications where electrical insulation is required, the inorganic particles are made of zinc oxide, titanium oxide, cesium oxide, which have no electrical conductivity. , Antimony oxide, tin oxide, indium tin oxide, yttrium oxide, lanthanum oxide, zirconium oxide, aluminum oxide, magnesium oxide, silicon oxide and other metal oxides, lithium fluoride, magnesium fluoride, aluminum fluoride, ice crystals Metal fluoride such as stone, metal phosphate such as calcium phosphate, carbonate such as calcium carbonate, sulfate such as barium sulfate and magnesium sulfate, nitride such as silicon nitride, boron nitride and carbon nitride, wollastonite, sepiolite Silicates such as zonotlite, titanates such as potassium titanate, etc. Arbitrariness.
The content of inorganic particles in the insulating sheet of the present invention is preferably 20% by volume or more and 85% by volume or less with respect to the entire insulating sheet. When the inorganic particle content is within 20% by volume, the heat dissipation performance when used as a heat dissipation sheet may be insufficient, and the operation efficiency of the device may be reduced, or the life of the material may be reduced. When the inorganic particle content exceeds 85% by volume, the insulating sheet may be broken at the time of processing or use, and the handleability may be deteriorated. The inorganic particle content is more preferably 30% by volume to 80% by volume, and still more preferably 40% by volume to 80% by volume.

In addition, the average particle diameter D2 of the inorganic particles is set to 0. 0 from the viewpoint of efficiently filling the gaps between the fibrous materials.
It is preferably 1 μm or more and 20 μm or less, more preferably 0.5 μm or more and 10 μm, and still more preferably 1 μm or more and 5 μm or less.
Here, the average particle diameter D2 of the inorganic particles means that the fibrous material and the binder resin part are removed from the insulating sheet by the plasma low-temperature ashing method to expose the inorganic particles. The treatment conditions are such that the resin is ashed but the inorganic particles are not damaged as much as possible. The inorganic particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer to determine the diameter of the equivalent circle diameter. The SEM magnification was 500 times, the observation spot was changed, the diameter of the equivalent circle diameter of 1000 particles was measured, and the average value was taken as the average particle diameter (μm). Average equivalent circle diameter Df (μm)
The average fiber diameter D1 (μm) of the fibrous material of the present invention and the average particle diameter D2 (μ
m) preferably satisfies 2 ≦ D1 / D2 ≦ 10, more preferably 2 ≦ D1 / D2 ≦ 8, and even more preferably 2 ≦ D1 from the viewpoint of efficiently filling inorganic particles into the gaps of the fibrous material. / D2 ≦ 6.

The binder resin contained in the insulating sheet of the present invention is preferably an organic binder typified by phenolic, silicone-based, acrylic-based, polyimide-based, epoxy-based or the like in order to give strength to the insulating sheet. Among these, an epoxy type is particularly preferable from the viewpoint that both adhesion and insulation properties when used as an insulating sheet can be achieved. Furthermore, the epoxy resin is preferably a crystalline epoxy resin from the viewpoint of increasing the flow characteristics and mechanical strength after curing and reducing the thermal expansion coefficient. The crystalline epoxy resin is an epoxy resin having a mesogen skeleton such as a biphenyl group, a naphthalene skeleton, an anthracene skeleton, a phenylbenzoate group, or a benzanilide group.
The shape of the binder resin contained in the insulating sheet of the present invention may be fibers, powders, emulsions, aqueous solutions, etc., but any binder can be used by selecting an appropriate addition method. Addition method is internal addition method, binder fiber or powder is added to the raw material slurry of the fibrous material and mixed, and external addition method is a method of spraying the emulsion or aqueous solution as a spray on the fibrous material, and paper making There are a method of impregnating a fibrous material with a binder solution consisting of an emulsion or an aqueous solution, a method of coating a paper-made fibrous material with a binder solution consisting of an emulsion or an aqueous solution, and combinations thereof are also conceivable, any of which may be used .

Next, a typical production method of the present invention will be described, but the present invention is not limited to this.
The method for producing the fiber constituting the fibrous material of the present invention is preferably a method in which the fiber is melted above the melting point of the polyphenylene sulfide and spun from the spinneret to form a fiber. The spun fiber is an unstretched polyphenylene sulfide fiber as it is. Most of the unstretched polyphenylene sulfide has an amorphous structure and an orientation parameter of less than 1.5, and can act as a binder for bonding fibers by applying heat.
On the other hand, since such fibers have poor dimensional stability due to heat, orientation parameters can be obtained by hot drawing at a temperature of not less than the glass transition temperature of polyphenylene sulfide and not less than glass transition temperature and not more than 50 ° C. 1.1 times or more after spinning. Becomes 1.5 or more, and the drawn yarn has improved strength and thermal dimensional stability. There are several commercially available products such as “Torcon” (registered trademark) (manufactured by Toray) and “Procon” (registered trademark) (manufactured by Toyobo).
The fibrous material of the present invention is preferably a wet nonwoven fabric made of polyphenylene sulfide fibers, which includes unstretched polyphenylene sulfide fibers in a part of the polyphenylene sulfide fibers, and the unstretched polyphenylene sulfide fibers are fused to form a nonwoven fabric. It is preferable. Heating by using an unstretched polyphenylene sulfide fiber as a part of the polyphenylene sulfide fiber is preferable because the fibers constituting the nonwoven fabric can be fixed to each other and the tensile breaking strength of the nonwoven fabric can be improved.

  The following method can be illustrated as a specific method for producing the nonwoven fabric. First, polyphenylene sulfide fibers (stretched polyphenylene sulfide fibers, unstretched polyphenylene sulfide fibers) are dispersed in water to form a papermaking slurry.

  The total amount of polyphenylene sulfide fibers based on the entire papermaking slurry is preferably 0.005 wt% or more and 5 wt% or less. By making the total amount 0.005% by weight or more, water can be efficiently used in the paper making process. Moreover, by making it 5 wt% or less, the dispersion state of the fibers is improved, and a uniform nonwoven fabric can be obtained.

  The papermaking slurry may be prepared by separately preparing a stretched polyphenylene sulfide fiber slurry and an unstretched polyphenylene sulfide fiber slurry in advance, and then mixing them with a paper machine, or making a slurry containing both directly. Good. It is preferable to make the slurry of each fiber separately and then mix the two in terms of being able to control the stirring time according to the shape and characteristics of each fiber separately. It is preferable in terms of simplicity.

  In order to improve the dispersion state, the papermaking slurry may be added with a dispersing agent or oil agent composed of a cationic, anionic or nonionic surfactant or an antifoaming agent that suppresses the generation of bubbles. Good.

The papermaking slurry prepared as described above is paper-made using a round-mesh type, long-mesh type, inclined net-type paper machine or hand-made paper machine, which is dried with a Yankee dryer, a rotary dryer, etc. can do.
The content of unstretched polyphenylene sulfide fibers constituting the wet nonwoven fabric is such that 20% by weight or more and 100% by weight or less of the total polyphenylene sulfide fibers are unstretched polyphenylene sulfide fibers from the viewpoint of firmly fusing the fibers together. More preferably, it is 25 to 100 weight%, More preferably, it is 25 to 75 weight%.
The fibrous material of the present invention is preferably subjected to a heating / pressurizing treatment from the viewpoint of firmly fusing the fibers together. Any method may be used for the heating / pressurizing treatment, and for example, heat pressing in a flat plate processing, calendar processing, or the like can be employed. Among these, a calendar process that can be continuously processed is preferable. As the calendering roll, a metal-metal roll, a metal-paper roll, a metal-rubber roll, or the like can be used. The temperature condition of the heating / pressurizing treatment should be not less than the glass transition temperature of the unstretched polyphenylene sulfide fiber and not more than the melting point, preferably not less than 88 ° C and not more than 250 ° C, more preferably not less than 88 ° C and not more than 220 ° C. is there. When the treatment temperature is lower than 88 ° C., the fibers are not sufficiently fused to each other, and a wet nonwoven fabric having low strength is obtained. On the other hand, if it exceeds 250 ° C., the unstretched polyphenylene sulfide fiber is too soft and sticks to a heating / pressurizing device such as a roll of a calendering machine or a hot press plate, and cannot be stably mass-produced. The pressure when calendering is employed as the heating / pressurizing treatment is preferably 10 kgf / cm or more and 720 kgf / cm or less. By setting it to 10 kgf / cm or more, fibers can be fused with sufficient strength. On the other hand, by setting it to 720 kgf / cm or less, it is possible to prevent the wet nonwoven fabric from being broken in the heating / pressurizing treatment and to stably perform the treatment.
Next, a method of adding inorganic particles and a binder to a fibrous material made of polyphenylene sulfide obtained by the above method will be described.

As a method for adding the inorganic particles of the present invention to a fibrous material, a method of melting the polyphenylene sulfide at a melting point or higher and spinning it from a spinneret into a fibrous material is supplied together with the polyphenylene sulfide and melt spinning. Examples thereof include a method of taking out a fiber and a step of making a fibrous material, a method of adding to a papermaking slurry, a method of dispersing and impregnating in a binder resin, and the like.
As a method for adding the binder resin of the present invention to the fibrous material, a coating method having high versatility and good workability is preferably used. Hereinafter, a method of adding a binder resin containing inorganic particles to a fibrous material by a coating method will be described by taking as an example the case where the binder resin containing inorganic particles is a polyimide resin and an epoxy resin.

  After the binder resin is dissolved in a solvent, it is applied to a fibrous material and dried to obtain an insulating sheet. What is necessary is just to select suitably what melt | dissolves binder resin as a solvent used here, for example, acetone solvent, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, ether solvent 1,4-dioxane, tetrahydrofuran, Diglyme, glycol ether solvent methyl cellosolve, ethyl cellosolve, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, diethylene glycol methyl ethyl ether, other benzyl alcohol, propanol, N-methylpyrrolidone, γ-butyrolactone, acetic acid Examples include ethyl, N, N-dimethylformamide and the like. In particular, when a solvent having a boiling point of 120 ° C. or lower under atmospheric pressure is included, desolvation is facilitated at a low temperature in a short time.

  The method of filling the binder with inorganic particles is not particularly limited, but after mixing polyimide resin, epoxy resin and inorganic particles in the above solvent using a propeller stirrer, homogenizer, kneader, etc., inorganic particles From the viewpoint of improving the dispersibility, it is preferable to mix by a bead mill, a ball mill, a three roll mill or the like.

  As a method of applying a binder or a composition comprising a binder and inorganic particles to a fibrous material, spin coating using a spinner, spray coating, roll coating, screen printing, or blade coater, die coater, calendar coater, meniscus coater And a coating method using a bar coater, a roll coater, a comma roll coater, a gravure coater, a screen coater, a slit die coater and the like.

  As the coating machine, a roll coater, comma roll coater, gravure coater, screen coater, slit die coater, etc. can be used. Is done.

  An oven, a hot plate, infrared rays, or the like can be used for drying. What is necessary is just to set a drying temperature and drying time suitably in the range which can volatilize an organic solvent. Specifically, it is preferable to hold for 1 minute to several tens of minutes in the range of 40 ° C to 120 ° C. Moreover, you may heat up in steps, combining these temperatures.

[Characteristic measurement method and effect evaluation method]
The characteristic measuring method and the effect evaluating method in the present invention are as follows.

(1) Glass transition temperature (Tg), melting point (Tm)
A sample of 5 mg was taken from the fibrous material, and the endothermic melting curve when the temperature was increased from −30 ° C. to 320 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter DSCII type manufactured by Seiko Instrument Co., Ltd. The peak temperature was taken as the melting point (Tm). Moreover, the glass transition temperature (Tg) was measured on the same measurement conditions.

(2) Insulation sheet thickness (μm)
The thickness of the insulating sheet was measured using a dial gauge thickness meter (manufactured by Mitutoyo Corporation) with a flat tip. The measurement was carried out 10 times at different locations, and the average value was taken as the thickness of the insulating sheet.

(3) Thickness direction thermal diffusion coefficient of insulating sheet (m ² / s)
Aluminum was vapor-deposited on both surfaces of the insulating sheet using a bell jar type vapor deposition machine. The vapor deposition thickness was set such that laser light from a laser pointer was irradiated from one side of the film, and the laser light was not transmitted through visual observation from the opposite side. Next, a laser light absorbing spray (Fine Chemical Japan Co., Ltd. Black Guard Spray FC-153) was applied thinly on both sides and dried, then a 10 mm square sample was cut out and LFA467 Nanoflash made by NETZSCH, which is a Xe flash analyzer. The thermal diffusivity α (m ² / s) in the film thickness direction was measured at a measurement temperature of 25 ° C. The measurement was performed 10 times with different samples, and the average value was used as the thermal diffusivity.

(4) Dielectric breakdown voltage (kV / mm)
The insulation sheet was cut into a square of size 25 cm × 25 cm, conditioned for 24 hours in a room at 23 ° C. and 65% Rh, and then subjected to an AC dielectric breakdown tester (made by Kasuga Denki Co., Ltd.) based on JIS C2151 (2006). AC 30 kV), the dielectric breakdown voltage (kV / mm) per unit thickness was measured at a frequency of 60 Hz and a boosting rate of 1000 V / sec.

(5) Orientation parameter of the fibrous material The fiber part of the fibrous material was measured with an inVIA micro-Raman spectrophotometer manufactured by RENISHA, with objective lens: 100 times, beam diameter: 1 μm, light source: second harmonic of YAG laser ( Measurement was performed as follows under the conditions of a wavelength of 532 nm), laser power: 100 mW, diffraction grating: Single 3000 gr / mm, slit: 65 μm, detector: CCD / RENISHA 1024 × 256.
The peak intensity of the Raman spectrum 1080 cm ⁻¹ band by irradiating the fiber part of the fibrous material with a laser beam perpendicular to the fiber axis and by the laser beam polarized in the fiber length direction and the laser beam polarized in the fiber diameter direction Were determined as Iyy and Ixx, respectively, and the ratio was determined as an orientation parameter RI = Iyy / Ixx. The measurement was performed on 20 fibers, and the average value was obtained by dividing the fiber into those of less than 1.5 and those of 1.5 or more.
For taking out the fiber portion of the fibrous material, cut out a plurality of insulating sheets, observe the cross section with a scanning electron microscope at a magnification of 100 times, and measure about 20 fiber portions that can be irradiated with laser light substantially parallel to the cross section and perpendicularly. went.

(6) Average fiber diameter D1 (μm)
10 images are taken at a magnification of 2000 times with a scanning electron microscope at 10 arbitrary positions of the fibrous material, and the diameter of any 15 fibers per image (however, it covers the fibers forming the fusion point) Thus, a portion where a film whose thickness is thinner than the fiber diameter of the fiber forming the fusion point is not measured), and this is performed on 10 images, and a total of 150 measurement results The average fiber diameter D1 was measured.

(7) Average particle diameter D2 (μm)
The fibrous material and the binder resin part are removed from the insulating sheet by a plasma low-temperature ashing method to expose the inorganic particles. The treatment conditions are such that the resin is ashed but the inorganic particles are not damaged as much as possible. The inorganic particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer to determine the diameter of the equivalent circle diameter. The magnification of SEM was 500 times, the observation spot was changed, the diameter of the equivalent circle diameter of 1000 particles was measured, and the average value was taken as the average particle diameter D2 (μm).

(8) Weight per unit area (g / m ² )
The wet nonwoven fabric and the insulating sheet were cut into a size of 20 cm × 20 cm, and the weight was measured and converted into a weight per 1 m ² .

(9) Heat dissipation as an insulating material The insulating sheet was cut into a 10 cm square size, and a plurality of sheets were overlapped so that the total thickness was in the range of 2 to 3 mm to obtain a laminate. In addition, when superimposing, between each layer, heat dissipation grease was apply | coated thinly and the layers were stuck. Laminate is placed on a 3cm diameter surface heat source (3.5W) placed at room temperature of 25 ° C, and after 5 minutes, the laminate is on the opposite side of the heat source using thermography (Nippon Avionics). The body surface temperature (surface temperature at a position perpendicular to the center of the heat source) was measured, and the temperature was defined as T (° C.). The observation temperature at the center of the heat source measured without placing the laminate on the heat source (the focus position of the observation point of the thermography is maintained with the laminate placed) is T0 (° C), and according to the following criteria The heat dissipation was evaluated. A is suitably used as an insulating material with high heat dissipation.
A: T-T0 is 2 ° C. or more D: T-T0 is less than 2 ° C. (10) Workability Flexibility as an index of workability was determined by the following method. The laminated sheet was subjected to a mandrel (flexibility) test at a room temperature of 25 ° C. by a method according to JIS K5600. The workability was evaluated according to the following criteria based on the diameter at which cracks and fractures occurred. A and B are practical ranges.

A: Bending radius causing cracks and breaks is less than 2 mm B: Bending radius causing cracks and breaks is 2 mm or more and less than 3 mm D: Bending radius causing cracks and breaks is 3 mm or more.

(11) Insulation The insulating sheet was cut into a circle having a diameter of 2 cm, and a plurality of sheets were overlapped so that the total thickness was in the range of 2 to 3 mm to obtain a laminate. In addition, when superimposing, between each layer, heat dissipation grease was apply | coated thinly and the layers were stuck. Next, two disc-shaped aluminum plates (surface roughness Ra = 100 nm) having a diameter of 2 cm and a thickness of 2 mm were prepared, and the laminate was sandwiched between the two aluminum plates, and the whole was heated as it was at 180 ° C. A pressure of 4 MPa was applied and thermocompression bonded for 1 hour. Then, after taking out from the press machine and cooling to room temperature and adjusting the humidity in a room at 23 ° C. and 65% Rh for 24 hours, an electrode is attached to the center of the disk of the front and back aluminum plates, and an AC dielectric breakdown tester is used. The dielectric breakdown voltage (kV) was measured. The insulation was evaluated according to the following criteria. A is a practical range.
A: Dielectric breakdown voltage is 100 kV or more D: Dielectric breakdown voltage is less than 100 kV (12) Hydrolysis resistance The insulation sheet is cut into a rectangular shape having a length of 150 mm and a width of 10 mm in the length direction and the direction perpendicular to the length direction. Sample a. In addition, the insulating sheet was left in a constant temperature and humidity chamber under an atmosphere of 45 ° C. × 90% Rh for 48 hours, and then cut into a rectangular shape having a length of 150 mm × width of 10 mm to obtain a sample b. These samples were subjected to a tensile test using a tensile tester (Orientec Tensilon UCT-100) with an initial tensile chuck distance of 50 mm and a tensile speed of 300 mm / min. The elongation at break (elongation) was determined from the obtained load-strain curve. In addition, the measurement was performed 5 times for each sample, and the average value was evaluated.
From the elongation of the obtained sample a and sample b, the elongation retention was obtained by the following formula and evaluated according to the following criteria. A is a practical range.

Elongation retention (%) = (sample b elongation / sample a elongation) × 100
A: Elongation retention 80% or more D: Elongation retention 80% or less (13) Heat resistance The insulating sheet is cut into a rectangular shape having a length of 150 mm and a width of 10 mm in the length direction and the direction perpendicular to the length direction. Sample a. In addition, the insulating sheet was left in a hot air oven at 200 ° C. for 250 hours, and then cut into a rectangular shape having a length of 150 mm and a width of 10 mm to obtain a sample b. These samples were subjected to a tensile test using a tensile tester (Orientec Tensilon UCT-100) with an initial tensile chuck distance of 50 mm and a tensile speed of 300 mm / min. The elongation at break (elongation) was determined from the obtained load-strain curve. In addition, the measurement was performed 5 times for each sample, and the average value was evaluated.
From the elongation of the obtained sample a and sample b, the elongation retention was obtained by the following formula and evaluated according to the following criteria. A is a practical range.

Elongation retention (%) = (sample b elongation / sample a elongation) × 100
A: Elongation retention 80% or more D: Elongation retention 80% or less

  Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited to these.

The raw materials used in the production examples, examples, and comparative examples of the present invention are as follows. In addition, the following wet nonwoven fabric, binder resin, and inorganic particle were used for the manufacture example, the Example, and the comparative example.
(Making wet nonwoven fabric)
[Stretched polyphenylene sulfide fiber]
As the stretched polyphenylene sulfide fiber, a fiber having an orientation parameter, an average fiber diameter, and a cut length of 6 mm shown in Table 1 was used.
[Dispersion of stretched polyphenylene sulfide fiber]
The above-mentioned stretched polyphenylene sulfide fiber was prepared so that the finished weight was as shown in Table 1, and both the stretched polyphenylene sulfide fiber and water were put into a household juicer mixer and stirred repeatedly to obtain a dispersion. It was. The stirring time was 10 seconds in order to prevent the fibers from getting tangled.

[Unstretched polyphenylene sulfide fiber]
As the unstretched polyphenylene sulfide fiber, a fiber having an orientation parameter, an average fiber diameter, and a cut length of 6 mm shown in Table 1 was used.
[Dispersion of unstretched polyphenylene sulfide fiber]
Prepare the unstretched polyphenylene sulfide fiber in the same manner as the stretched polyphenylene sulfide fiber so that the finish is the basis weight shown in Table 1, and put the stretched polyphenylene sulfide fiber and water into a household juicer mixer. Stirring was repeated to obtain a dispersion. The stirring time was 10 seconds in order to prevent the fibers from getting tangled.

[Paper]
In each of the examples and comparative examples, a size of 25 cm in which a 140-mesh handmade papermaking net is installed at the bottom of a dispersion obtained by blending stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers shown in Table 1 at a ratio shown in Table 1. × 25cm, 40cm in height handmade paper machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) was added so that the finished weight was as shown in Table 1, and water was added to make the total amount of the papermaking dispersion 20L. Stir thoroughly with a vessel. Next, water from the handmade paper machine was drained, and the wet paper remaining on the papermaking net was transferred to filter paper.

[Dry]
The wet paper is put into a rotary dryer together with the filter paper, and the process of drying at a temperature of 140 ° C., a process passing speed of 0.5 m / min, and a process length of 1.25 m (processing time of 2.5 minutes) is repeated twice. The wet nonwoven fabric shown in Table 1 after drying was obtained.

[Heating / pressurizing]
The wet nonwoven fabric subjected to the drying treatment was peeled off from the filter paper and passed through a calendar processing machine (manufactured by Yuri Roll Co., Ltd.) consisting of a metal roll and a paper roll. The calendar conditions were a temperature of 160 ° C., a pressure of 345 kgf / cm, and a roll rotation speed of 5 m / min.

(Solvent) MEK: Methyl ethyl ketone
(Binder resin)
JER828: Bisphenol A type liquid epoxy resin (Mitsubishi Chemical Corporation)
HP4032: Epoxy resin having a naphthalene skeleton (manufactured by DIC Corporation)
(Curing agent)
2P4MZ: 2-phenyl-4-methylimidazole (inorganic particles)
AO509: Alumina particles (average particle size: 10 μm) (manufactured by Admatechs Co., Ltd .: trade name Admatechs)
AO502: Alumina particles (average particle size: 0.7 μm) (manufactured by Admatechs Co., Ltd .: Trade name Admatechs)
Examples 1-12, Comparative Examples 1-4
80 g of MEK, 16 g of HP4032, 24 g of JER828, and 3.0 g of 2P4MZ were mixed and stirred, and the addition amount shown in Table 2-1 was added to AO509 or AO502, and the mixture was further stirred to obtain an average particle diameter D2. An inorganic particle-containing binder resin was obtained.
The inorganic particle-containing binder resin having an average particle diameter D2 thus obtained was coated on a fibrous material having an average fiber diameter D1 and a basis weight shown in Table 1 using a slit die coater. The obtained fibrous material was dried at 130 ° C. for 30 minutes to cure the inorganic particle-containing binder resin to obtain an insulating sheet.
In the examples, the insulating sheet manufactured by the above steps has a thickness, a thermal diffusivity in the thickness direction, and a dielectric breakdown voltage as shown in Table 2-2. showed that. Moreover, in a comparative example, it was thickness, the thermal diffusivity of a thickness direction, and a dielectric breakdown voltage as shown in Table 2, and the property which was inferior in workability and inferior as a heat-radiation sheet was shown.

Comparative Examples 5-8
The single fibrous material shown in Table 1 has a thickness, a thermal diffusivity in the thickness direction, and a dielectric breakdown voltage as shown in Table 2-2, and exhibited poor properties as a heat dissipation sheet.

Comparative Examples 9-12
In Example 1, the heat-radiation sheet was obtained similarly except not adding an inorganic particle. The obtained insulating sheet had a thickness, a thermal diffusivity in the thickness direction, and a dielectric breakdown voltage as shown in Table 2-2. Although the workability was good, the heat insulating sheet showed inferior characteristics.

Comparative Examples 13 and 14
In Example 1, except that a fibrous material was not used, a binder resin containing inorganic particles was cured in the same manner to obtain a heat radiating sheet. The obtained insulating sheet had a thickness, a thermal diffusivity in the thickness direction, and a dielectric breakdown voltage as shown in Table 2-2, and exhibited poor properties as an insulating sheet.

Comparative Examples 15 and 16
In the fibrous material shown in Table 1, an inorganic sheet of AO509 or AO502 was added in the amount shown in Table 2 without using a binder resin, but an insulating sheet was obtained, but the inorganic particles dropped off, and an insulating sheet was obtained. There wasn't.

The meanings of the abbreviations in the table are as follows: PPS: Polyphenylene sulfide

Claims (6)

An insulating sheet containing a fibrous material, inorganic particles, and a binder resin, and satisfying the following (i) to (iii).
(I) Thickness is 20 μm or more and 400 μm or less (ii) Thermal diffusivity in thickness direction is 1 × 10 ⁻⁷ m ² / s or more (iii) Dielectric breakdown voltage is 25 kV / mm or more The insulating sheet according to claim 1, wherein the fibrous material is made of polyphenylene sulfide. The insulating sheet according to claim 1, comprising a fibrous material having an orientation parameter of less than 1.5 and a fibrous material having an orientation parameter of 1.5 or more. The insulating sheet according to any one of claims 1 to 3, wherein an average fiber diameter D1 of the fibrous material is 5 µm or more and 50 µm or less. The insulating sheet according to any one of claims 1 to 4, wherein an average particle diameter D2 of the inorganic particles is 0.1 µm or more and 20 µm or less. The insulating sheet according to any one of claims 1 to 5, wherein an average fiber diameter D1 (μm) of the fibrous material and an average particle diameter D2 (μm) of the inorganic particles satisfy 2 ≦ D1 / D2 ≦ 10.